Glass melting gurnace and method for producing glass

ABSTRACT

A charged glass raw material B is melted in a melting tank  10  by heating with a burner  31  and by heating with electrodes  12 , to form molten glass G. Then, the molten glass G flows into a tank additionally provided as a noble gas dissolving tank  20  through a throat  40 . The noble gas dissolving tank  20  is provided with a noble gas dissolving device  53 , and the noble gas dissolving device  53  is provided with sixteen noble gas inlets  22  for introducing a helium or neon gas supplied to a hearth through heat resistant gas introduction tubes  21  into the noble gas dissolving tank  20 . Bubbles of a helium gas A having a purity of 99% are blown out from the noble gas inlets  22  in volumes such that the bubbles have an average diameter of 80 mm or less in the molten glass G.

TECHNICAL FIELD

The present invention relates to a glass melting furnace capable ofimproving homogeneity of a glass product by reducing bubble defects inglass, and to a method of manufacturing glass using the glass meltingfurnace.

BACKGROUND ART

Over many years, glass manufacturing industry has aimed at manufacturinghomogeneous glass products containing no contaminants, bubbles, and thelike through melting at high efficiency, and supplying glass productsthat meet demands. The glass manufacturing industry has attempted toattain an object of manufacturing homogeneous glass in various glassproducts, and numerous inventions have been made to attain the object.Although factors causing inhomogeneous glass such as stones, cords, andprecipitation of heterogeneous crystals in glass can be eliminated, anobject of removing bubbles completely remains unattained. The removal ofbubbles generally employs a method involving: addition of fining agentsin a raw material composition; expansion and elevation of bubbles ofvery small diameters through a redox reaction of fining agents; anddeaeration of the bubbles from molten glass.

As shown in FIG. 11, in general, a glass melting furnace for performingcontinuous production of glass is often constituted by a melting tank 10for melting glass by heating, and a fining chamber 30 for deaeratingbubbles from molten glass G after the melting. In such a continuousproduction method, a glass raw material B including various glass rawmaterial powder and glass cullet is homogeneously mixed in advance, andthe glass raw material B is continuously charged from an inlet 11 in themelting tank 10 of the melting furnace formed of a refractory materialR. Inside of the melting tank 10 is heated to high temperatures by aburner 31 and an electrode 12 for a vitrification reaction of the glassraw material B. Then, oxygen bubbles and the like are generated througha redox reaction of fining agents added into the glass raw material B inthe fining chamber 30 connected to the melting tank 10, to expandbubbles having very small diameters of a carbon dioxide gas and the likegenerated during the vitrification reaction and to elevate the bubblesto a surface of the molten glass G for fining. Thereafter, the moltenglass G is homogenized with a stirrer 51 provided in a feeder 50, formedinto a predetermined shape in a forming part, and annealed into a glassproduct.

When continuous production is not performed, the production is performedin a so-called batch production furnace employing a crucible of quartz,alumina, or the like, a crucible of another refractory material, or avessel (pot) formed of a heat resistant metal containing platinum asshown in FIG. 12. In this case, molten glass is homogenized throughprocesses of melting and fining in one tank. To be specific, glass rawmaterials are charged into a refractory vessel 70 protected by arefractory material R and provided inside the refractory material R. Theglass raw materials in the heat resistant vessel 70 are indirectlyheated by a heating element 41. A series of processes including finingis performed in the same tank for the molten glass G produced through avitrification reaction. The molten glass G is homogenized with a stirrer51, and is allowed to flow out from an outlet 60 provided at a bottom ofa melting tank. The molten glass G is formed into a predetermined shapeand annealed into a glass product.

In order to attain an object of more assuredly fining bubbles, which aredefects generated in the molten glass, Patent Document 1 describes amethod of deaerating bubbles of very small diameters by introducing agas such as air, oxygen, or argon as bubbles into the molten glassthrough a bubbling nozzle provided in the above-described finingchamber. Further, Patent Document 2 discloses a technique referred to asvacuum degassing for deaerating bubbles in the molten glass forhomogenization by intentionally adjusting a pressure of a glass meltingatmosphere to a pressure lower than an atmospheric pressure.

Further, Patent Document 3 describes use of a helium atmosphere forremelting a glass cullet to prevent reboiling of bubbles. However,Patent Document 3 includes no description regarding an effective heliumcontent in glass or the like, and lacks detail. Patent Document 4describes the use of helium in a dry gas to be bubbled. However, PatentDocument 4 includes no description regarding specific modes of abubbling device or a helium content in glass, and thus cannot be appliedto a glass manufacturing apparatus allowing mass production. PatentDocument 5 also describes the use of helium bubbling. However, PatentDocument 5 includes no specific description regarding a device forbubbling helium or a helium content in glass, and thus cannot be appliedto a glass manufacturing apparatus allowing mass production.

[Patent Document 1] Japanese Utility Model Registration No.

[Patent Document 2] JP-A 2000-239023

[Patent Document 3] JP-A 06-329422

[Patent Document 4] JP-A 07-172862

[Patent Document 5] U.S. Pat. No. 3,622,296

DISCLOSURE OF THE INVENTION

Various melting furnaces obtained by improving a melting furnace shownin FIG. 11 or 12 have been disclosed as melting furnaces acceleratingdeaeration of bubbles from molten glass by use of fining agents.However, the melting furnaces are subjected to restrictions by variousfactors such as use, a production, a glass material, and a glass rawmaterial, and are far from melting furnaces capable of homogenizingmolten glass efficiently. A method of adding fining agents to glass rawmaterials is easily employed without question, but careful studies arerequired on various factors such as the type or amount of fining agents,a glass material to be added, and a heating method. Even if optimalselections of the factors are made once, there are disadvantages in thatthe factors are apt to be affected by a glass flow rate, a meltingtemperature, a melting atmosphere, and the like. Some of the finingagents provide large influences such as environmental problems and arehardly added in large amounts.

Stirring through bubbling employing a bubbling nozzle or stirring with astirrer is often combined with other methods, and the use of stirringalone leaves concerns. The stirring method is rather useful means foraiding a deaeration effect by the above-described fining agents and anauxiliary method for enhancing the effect in combined use with othermethods, and has not yet reached a level of realizing large effects inuse of the method alone.

A technique of accelerating deaeration of bubbles from the molten glassby applying a pressure reducing technique or vacuum technique to themolten glass at high temperatures involves removal of bubbles from themolten glass and easy partial loss of molten glass components throughvaporization at the same time. Thus, environmental problems associatedwith collection of the molten glass components and problems such asdegradation of the device itself by vaporized substances are pointedout. Further, a large device is required for treating a large volume ofmolten glass, but precise maintenance of a reduced pressure or vacuumenvironment involves problems in that precise and continual maintenanceis required.

The inventors of the present invention have conducted extensive studiesin view of the above circumstances, and an object of the presentinvention is therefore to provide: a glass melting furnace allowingstable mass production of molten glass without bubbles through a methodof manufacturing glass through melting, which is the most generally usedmethod in glass manufacturing industry; and a method of manufacturingglass using the glass melting furnace.

That is, the glass melting furnace of the present invention is a glassmelting furnace for melting glass raw materials by heating to formmolten glass, characterized by including: an inlet for charging glassraw materials; an outlet for taking out molten glass; a melting tank forretaining the glass raw materials and the molten glass for apredetermined period of time; heating means for heating the glass rawmaterials and molten glass charged into the melting tank; and noble gasdissolving means for supplying helium and/or neon from a noble gasinlet, and diffusing and mixing helium and/or neon into the molten glassto dissolve a predetermined concentration or more of helium and/or neonin the molten glass.

In the above-described constitution, the inlet for charging the glassraw materials and the outlet of the molten glass may be shared, or aplurality of each may be provided. The heating source may employ amethod through electricity, burning of various fuels, electromagneticwave, or the like. One method may be used alone, or a plurality ofmethods may be used in combination for heating. Any heating device forcontrolling heating can be used without particular limitation as long asit is a device having no reactivity inhibiting a vitrification reaction,causing no problems in structural strength at high temperatures, havinga size allowing heating of glass raw materials at once in a volume inaccordance with the purpose, and constructed with construction materialsin accordance with the purpose of melting a glass material.

The supply of helium and/or neon into the molten glass may be continuesor intermittent. The glass melting furnace may be provided with one or aplurality of noble gas inlets for supplying helium and/or neon. Asectional shape of the noble gas inlet is not particularly limited.

The noble gas dissolving means is for: diffusing helium and/or neon inan atomic state into glass in a molten state; mixing helium and/or neonto disperse homogeneously; and dissolving helium and/or neon in anetwork structure formed of elements constituting the glass and having arelatively large bonding strength such that helium and/or neon exists ina trapped state without being bonded to the network structure. The noblegas dissolving means is actually provided to connect to the meltingsurface directly or indirectly.

The size or shape of the noble gas dissolving means is not particularlylimited as long as the above-described functions are realized. One noblegas dissolving means may be provided, or a plurality thereof may be usedin combination in accordance with a production of glass, for example.

Further, the phrase “dissolving a predetermined concentration or more ofhelium and/or neon” specifically indicates dissolving of helium and/orneon in the molten glass such that a concentration of helium and/or neonis 0.0001 μl (microliter)/g (0° C., 1 atm) or more, preferably 0.001μl/g (0C, 1 atm), more preferably 0.01 μl/g (0C, 1 atm) in the moltenglass.

Further, the glass melting furnace of the present invention ischaracterized in that the noble gas dissolving means is at leastpartially immersed in the molten glass, in addition to theabove-described constitution.

Here, the phrase “noble gas dissolving means is at least partiallyimmersed in the molten glass” indicates that the noble gas dissolvingmeans is used in a state of being partially or totally immersed in themolten glass.

Further, the glass melting furnace of the present invention ischaracterized in that the noble gas dissolving means is provided in atleast one position selected from the inside, upper side, lower side, andside of the molten glass, in addition to the above-describedconstitution.

The noble gas dissolving means is provided in at least one positionselected from the inside, upper side, lower side, and side of the moltenglass, to thereby assuredly diffuse or mix helium and/or neon into themolten glass. The noble gas dissolving means may be provided at aplurality of positions. For example, two noble gas dissolving means maybe provided with one provided on a side and the other provided on alower side. Alternatively, one noble gas dissolving means may beprovided to extend from a lower side to a side.

Further, the glass melting furnace of the present invention ischaracterized in that the noble gas dissolving means contains at leastone device selected from the group consisting of a heating device, apressure reducing device, and a centrifugal force generating device.

The heating device, the pressure reducing device, or the centrifugalforce generating device may be a part of a device having otherfunctions, or may realize those functions with other devices.

Embodiments of the heating device include: a burner for burningcombustible fuels such as hydrocarbons, oxygen, and hydrogen; aresistance heating element utilizing electricity; an electrode fordirect application of current; a dielectric heater utilizing highfrequency current; and an electromagnetic wave irradiator such as aninfrared irradiator. One heating device may be used, or a pluralitythereof may be used in combination in accordance with the type or use ofglass to be melted. The heating device is provided as a device separatefrom a heating device for glass melting. Any type of pressure reducingdevice may be employed as long as the device is capable of reducing apressure to an atmospheric pressure or less and has heat resistance. Anycentrifugal force generating device may be employed without particularlimitation as long as the device is capable of providing the moltenglass with centrifugal force generated through high-speed rotation.

Further, the glass melting furnace of the present invention ischaracterized in that the heating means is provide with at least onetank constituted by a heat resistant vessel, in addition to theabove-described constitution.

Here, the heat resistant vessel constituting the heating device musthave a sufficient level of heat resistance for preventing corrosion ofthe vessel through a chemical reaction with glass easily caused at hightemperatures etc.

The heat resistant vessel preferably has low reactivity with a meltingatmosphere and sufficient strength for retaining the molten glass athigh temperatures. To be specific, any material having high temperatureheat resistance including a metal material such as platinum or ceramicsmay be used, and a plurality of materials may be used in combination.

Further, the glass melting furnace of the present invention ischaracterized in that the noble gas dissolving means generates a flow ofa helium and/or neon gas in a direction at a vector angle of 0° to 800,500 to 130°, or 100° to 180° with respect to a flow direction of themolten glass.

Here, the phrase “flow of a helium and/or neon gas” indicates a flow ofhelium and neon perceived as a gas until helium and neon diffuse in themolten glass, not a flow of helium and neon in a state of monoatomicmolecules diffusing in the molten glass. That is, helium and neon areallowed to flow in a gas state at a specific flow angle with respect tothe flow of the molten glass from the melting tank toward a formingregion, to thereby realize faster diffusion and mixing than thoserealized by simply bringing both flows into contact with each other in astatic state.

Of the vector angles, a vector angle between the both flows set to 100to 180° provides particularly effective actions. Such a vector angle maybe effectively applied to a molten glass of a glass material having ahigh viscosity glass melt and a composition inhibiting actions of heliumand neon through bubbling or the like, and especially to molten glass ofa glass composition having a small alkali content or substantially noalkali content. Meanwhile, a vector angle between both flows set to 50to 130° may be applied to non-alkali glass, but provides moderatediffusion and mixing, and dissolution of atoms compared with those in acase employing a larger vector angle. In order to accelerate diffusionand mixing, and dissolution, other conditions such as temperature andpressure must be set more strictly. A vector angle between both flowsset to 0 to 80° may be applied to a glass material having a compositionwhich greatly facilitates diffusion and mixing of helium and/or neon.However, even with a glass material of a composition having a highviscosity inhibiting diffusion of helium and/or neon such as non-alkaliglass, helium and/or neon may be diffused and mixed into the moltenglass by using other homogenizing devices in combination.

Further, the glass melting furnace of the present invention ischaracterized in that the noble gas dissolving means is formed of a heatresistant metal and/or ceramics, in addition to the above-describedconstitution.

The noble gas dissolving means is used under a high temperatureenvironment, and may be used in a state of being immersed in the moltenglass as required. Thus, the noble gas dissolving means preferablyemploys a heat resistant metal having appropriate heat resistance andcorrosion resistance or ceramics.

The noble gas dissolving means preferably has the following functionsfor realizing its ability assuredly and rapidly. That is, the noble gasdissolving means preferably has functions including: a function ofheating a helium and/or neon gas before the gas is introduced into themolten glass; a function of precisely adjusting a flow rate of the gasto be introduced; a function of adjusting volumes of bubbles of theintroduced gas formed into bubbles in the molten glass; and a functionof mutually and finely adjusting each of the functions from otherphysical values such as set values or measured values of a furnacemolten glass temperature, a temperature of a refractory material, afurnace ambient pressure, a volume of a dissolved gas, a glass flowrate, and the like.

Here, the function of heating a helium and/or neon gas before the gas isintroduced into the molten glass is an important function for rapidlydiffusing and mixing the gas into the molten glass by heating the gasfor dissolution of the gas. To be specific, the function may employheating of the gas with a heating element for indirect heating, heatingthereof with a radiator, or the like. However, the simplest methodinvolves heat exchange with a waste gas while the waste gas is collectedfor efficient use of the waste gas and for effective operation in termsof energy balance. The function of precisely adjusting a flow rate ofthe gas to be introduced allows dealing with fluctuation in propertiesof a glass state due to furnace operation conditions through fineadjustment based on precise measurement of the flow rate. The functionof adjusting volumes of bubbles of the introduced gas formed intobubbles in the molten glass may be realized together with the functionof adjusting a flow rate of the gas. Further, the function may employ amethod of providing a jig for an intermittent gas flow at a positionwhere the molten glass and the gas are initially brought into contactwith each other. Further, devices such as adjustment of the size orshape of a gas outlet to suppress a bubble diameter as small as possiblemay be made. The function of mutually and finely adjusting each of thefunctions from other physical values such as set values or measuredvalues of a furnace molten glass temperature, a temperature of arefractory material, a furnace ambient pressure, a volume of a dissolvedgas, a glass flow rate, and the like allows maintenance of a finingstate of the molten glass in the furnace in an optimally controlledstate by establishing a system for monitoring the physical values asneeded. Based on the results of the monitoring system, automation of asystem for providing appropriate action by using a computer or the likeallows maintenance of stable manufacturing conditions with minimumlabor.

The heat resistant metal or ceramics to be used here must have lowreactivity with the molten glass at high temperature and low reactivitywith other construction materials or the like used in combination, inaddition to heat resistance. In particular, the heat resistant metal orceramics are exposed to a reaction gas or vaporized gas from the moltenglass for a long period of time, and a material must be selected inconsideration of reactivity with a gas phase or corrosion properties.

Further, the glass melting furnace of the present invention ischaracterized by further including noble gas degassing means fordegassing a gas containing helium and/or neon from the molten glassafter helium and/or neon is diffused and mixed into the molten metal,which is provided in at least one position selected from the inside,upper side, lower side, and side of the molten glass.

The noble gas degassing means provided in at least one position selectedfrom the inside, upper side, lower side, and side of the molten glassallows effective degassing of helium and/or neon diffused and mixed inthe molten glass from the molten glass, to thereby perform favorablefining of the molten glass. The noble gas degassing device is usefulwhen glass has a particularly high viscosity and a heavy burden isplaced on the melting device itself without degassing, or when anabsolute volume of a gas component in glass is very large and degassingis insufficient with a normal fining chamber. A mode of the noble gasdegassing device corresponds to that of the noble gas dissolving meansdescribed above, so the same descriptions are omitted.

Further, the glass melting furnace of the present invention ischaracterized in that the noble gas degassing means includes at leastone device selected from the group consisting of a heating device, apressure reducing device, and a centrifugal force generating device, inaddition to the above-described constitution.

The heating device, the pressure reducing device, and the centrifugalforce generating device may each have the same constitution as that ofthe noble gas dissolving means or a different constitution from that ofthe noble gas dissolving means.

That is, examples of the heating device include: a burner for burningcombustible gaseous fuels such as hydrocarbons, oxygen, and hydrogen, orcombustible liquid/solid fuels; a resistance heating element utilizingelectricity; an electrode for direct application of current; adielectric heater utilizing high frequency current; and anelectromagnetic wave irradiator such as an infrared irradiator. Oneheating device may be used, or a plurality thereof may be used incombination in accordance with the type or use of glass to be melted.The heating device is provided as a device separate from a heatingdevice for glass melting or devices constituting the noble gasdissolving means, or may be shared with other devices. Any type ofpressure reducing device may be employed as long as the device iscapable of reducing a pressure to an atmospheric pressure or less andhas heat resistance. The pressure reducing device is preferably providedwith a cooling function because performance of the device itself must bemaintained in the vicinity of the device at high temperature. Anycentrifugal force generating device may be employed without particularlimitation as long as the device is capable of imparting the moltenglass with centrifugal force generated through high speed rotation.

The above-described noble gas dissolving means or noble gas degassingmeans may operate on the molten glass at different times in time series,or the dissolving means and the degassing means may operate atsubstantially the same time. However, for operation at the same time,other environmental conditions for helium or neon to dissolve rapidlyinto the molten glass, that is, conditions such as a temperature, anatmosphere, and a pressure must be sufficiently adjusted.

Further, the glass melting furnace of the present invention ischaracterized in that the noble gas degassing means includes a noble gascollection chamber on an upper side the molten glass, in addition to theabove-described constitution.

Here, the term “noble gas collection chamber” is a space on an upperside of the molten glass and for temporarily accumulating helium or neondegassed from the molten glass.

The shape or size of the noble gas collection chamber is notparticularly limited as long as the chamber has a heat resistantstructure and is capable of maintaining a substantially airtight state.An upper space of the melting tank or fining chamber may be used as thenoble gas collection chamber, or a closed space provided separately fromthe melting tank, the fining chamber, or the like may be used as thenoble gas collection chamber. The noble gas collection chamber requiresa temperature measuring device, a dust collector, or the like. Further,the noble gas collection chamber may be connected to a gas separationdevice capable of collecting at high efficiency a noble gas such ashelium or neon from a high temperature mixed gas containing gases suchas carbon dioxide, steam, oxygen, and nitrogen generated through avitrification reaction, for using the noble gas again.

When the upper space of the molten glass in the heat resistant vessel isused as the noble gas collection chamber, the noble gas collectionchamber not necessarily needs to be provided over an entire region ofthe upper space, and may be provided in a part of the region. As aspatial positional relationship, the noble gas collection chamber needsnot be provided directly above the molten glass, and may be providedobliquely upward.

Further, the glass melting furnace of the present invention ischaracterized in that the noble gas dissolving means is provided with aplurality of noble gas inlets, in addition to the above-describedconstitution.

The advantages for the noble gas dissolving means provided with aplurality of noble gas inlets are described below. That is, in order toenhance an overall dissolved volume of a helium and/or neon gas intomolten glass when the noble gas is introduced into the molten glass, acontact interface between the noble gas and the molten glass must beexpanded. Even if a large volume of the noble gas is suppliedintermittently from one noble gas inlet, bubbles formed from the noblegas aggregate with one another into one large bubble while the bubbleselevate through the molten glass having a high viscosity. Thus, even ifa supply volume of the noble gas is increased, an area of contactinterface with the molten glass cannot be increased. In contrast, whenthe noble gas is supplied from the plurality of noble gas inlets, aphenomenon of the bubbles formed from the noble gas to aggregate into alarge bubble is suppressed, and most bubbles elevate through the moltenglass while maintaining small diameters. Thus, the area of contactinterface with the molten glass can be increased even with a relativelysmall supply volume of the noble gas, to thereby increase an overalldissolved volume of the noble gas into the molten glass.

Meanwhile, even if an excess number of noble gas inlets are provided forone glass melting furnace, a greatly accelerating effect on dissolutionof helium or neon in the molten glass is small considering labor orrequired cost. However, numerous noble gas inlets may be provided tofurther increase a dissolved volume of helium or neon if a burden suchas cost is not taken into consideration. Thus, the number of the noblegas inlets of helium or neon is in a range of preferably 2 to 100,000,more preferably 4 to 10,000, still more preferably 6 to 5,000, yet morepreferably 10 to 3,000, still yet more preferably 11 to 2,000,furthermore preferably 13 to 1,000, most preferably 15 to 500.

A density of the noble gas inlets provided is limited by diameters ofthe bubbles to be formed. When simple bubbling is employed, diameters ofbubbles to be formed are hardly adjusted to less than 1 cm, and aninterval between the noble gas inlets must be 1 cm or more. Thus, thedensity of the noble gas inlets provided must be 10,000 inlets/m² orless. The density is preferably 9,000 inlets/m² or less, more preferably8,000 inlets/m² or less, still more preferably 7,000 inlets/m² or less.When devices such as reducing of diameters of bubbles formed by applyinga mechanical shear force on the bubbles is made in addition to simplebubbling, the density of the noble gas inlets is 1,000,000 inlets/m² orless, preferably 900,000 inlets/m² or less, more preferably 800,000inlets/m² or less.

Further, the glass melting furnace of the present invention ischaracterized in that the plurality of noble gas inlets are provided ona hearth and/or on a furnace wall, in addition to the above-describedconstitution.

As described above, the noble gas inlets are preferably provided on aheat resistant hearth retaining the molten glass, or on a furnace wallcontinuing from the hearth. Obviously, the noble gas inlets may beprovided at a boundary between the hearth and the furnace wall.

Further, the glass melting furnace of the present invention ischaracterized in that the plurality of noble gas inlets are each formedof a metal having a melting point of 1,000° C. or higher, in addition tothe above-described constitution.

Such a constitution allows adjustment of a temperature where heliumand/or neon is brought into direct contact with the molten glass to hightemperatures of 1,000° C. or more.

Further, the glass melting furnace of the present invention ischaracterized in that the noble gas dissolving means is provided in anoble gas dissolving tank connected downstream of the melting tank, inaddition to the above-described constitution. A fining chamber may beconnected downstream of the noble gas dissolving tank.

A connecting part between the melting tank and the noble gas dissolvingtank may be: a heat resistant tube; a tilted tub; a part having afunction of allowing flow of glass melted in the melting tank to thenoble gas dissolving tank; or a wall surface dividing both tanks, havingproperties such as heat resistance and corrosion resistance, andprovided with a passage part. The connecting part is not limited to apart having a structural connecting part (bonding part), and only needsto have a structure allowing transfer of the molten glass from themelting tank to the noble gas dissolving tank as a result. For example,the connecting part may have a structure not structurally bonded, andallowing a steady flow of the molten glass overflowing from apredetermined position in the melting tank along a refractory rod-likestructure for directing the molten glass to the noble gas dissolvingtank. In this case, the refractory rod-like structure for directing themolten glass is provided in the melting tank, but is not directlyprovided in the noble gas dissolving tank downstream.

The noble gas dissolving tank preferably has an inner wall surfaceformed of a refractory brick having a refractory temperature of 1,200°C. or higher, or a heat resistant metal having a melting point of 1,200°C. or higher. To be specific, the inner wall surface of the noble gasdissolving tank is coated with the above-described refractory brick orheat resistant metal (or both of the refractory brick and heat resistantmetal). Such a constitution allows diffusion of helium or neon into themolten glass in an environment of 1,200° C. or higher, which thus allowsefficient dissolution of helium or neon in the molten glass.

The refractory brick having a refractory temperature of 1,200° C. orhigher may be an inorganic oxide, nitride, or the like having aplurality of components or a single component. A component ratio may bechanged as required, and a plurality of refractory bricks having totallydifferent components may be used in combination, to thereby improvehomogeneity of the molten glass having helium or neon dissolved therein.Further, the use of the plurality of refractory bricks in combinationmay prevent elution of components inhibiting elevation of bubbles intothe molten glass, and prevent a surface state in which fine bubbles areapt to be trapped at an interface between the refractory material andthe molten glass.

The heat resistant material having a melting point of 1,200° C. orhigher and having a plurality of metal components or a single metalcomponent may provide an environment without formation of unwantedbubbles in the glass not to inhibit diffusion and dissolution of heliumor neon, by taking into sufficient consideration, for example, itsreactivity with the molten glass. The reason for specifying the meltingpoint of 1,200° C. is that the melting point is required for allowingefficient dissolution of helium or neon in glass as described aboveregarding the refractory temperature.

Further, the glass melting furnace of the present invention ischaracterized in that the refractory brick contains at least oneselected from the group consisting of SiO₂, ZrO₂, Al₂O₃, MgO, Cr₂O₃, C,and WO₃, in addition to the above-described constitution.

Here, the refractory brick containing at least one selected from thegroup consisting of SiO₂, ZrO₂, Al₂O₃, MgO, Cr₂O₃, C, and WO₃ indicatesthat the refractory brick contains at least one of silica (or quartz orsilicon dioxide), zirconia (or zirconium oxide), alumina (or aluminumoxide), magnesia (or magnesium oxide), chromium oxide, carbon, andtungsten oxide.

SiO₂ may be used as a refractory material for melting optical glass orthe like. SiO₂ is a material having heat resistance appropriate forconstituting the noble gas dissolving tank for dissolving helium orneon, and is a suitable material for dissolving helium or neon intomolten glass having components of high purity. ZrO₂ is suitable fordissolving helium or neon into molten glass requiring high temperaturemelting at 1,500° C. or higher. Al₂O₃ is preferably used as aconstruction material (lining material) for the noble gas dissolvingtank similar to SiO₂. MgO and Cr₂O₃ are preferable for allowingconstruction of the noble gas dissolving tank at low building cost. C orWO₃ may be preferably used when helium or neon is dissolved in glassrequiring special components.

Further, the glass melting furnace of the present invention ischaracterized in that the heat resistant metal contains at least oneselected from the group consisting of Pt, Ir, Os, Re, W, Ta, Rh, Hf, Ru,Tc, Pd, Mo, Ti, Zr, and Nb, in addition to the above-describedconstitution.

Here, the heat resistant metal containing at least one selected from thegroup consisting of Pt, Ir, Os, Re, W, Ta, Rh, Hf, Ru, Tc, Pd, Mo, Ti,Zr, and Nb indicates that the heat resistant metal contains 1 mass % ofat least one component as a heat resistant metal material selected fromthe group consisting of platinum, iridium, osmium, rhenium, tungsten,tantalum, rhodium, hafnium, ruthenium, technetium, palladium,molybdenum, titanium, zirconium, and niobium. The metal material may beused alone or as an alloy, and different metal materials may be used inaccordance with a part to be used. A composite material of ceramics anda metal may also be used.

Further, the method of manufacturing glass of the present invention is amethod of manufacturing glass for melting glass raw materials by heatingto form molten glass, characterized by including: introducing bubblescontaining helium and/or neon and having an average diameter of 150 mmor less into molten glass; and diffusing and mixing helium and/or neoninto the molten glass to incorporate a predetermined volume of heliumand/or neon into the molten glass.

Bubbles containing helium and/or neon and having an average diameter of150 mm or less are formed to increase an area of contact interfacebetween helium or neon and the molten glass. The diameters of thebubbles are preferably small, and the number thereof is preferablylarge. However, the sizes and number of the bubbles for realizingeffective fining vary depending on a volume of glass. That is, for glasshaving a large volume, many bubbles with small diameters are preferablyformed. In contrast, bubbles having an average diameter of more than 150mm causes scattering of a molten glass material covering the bubbleswhen the bubbles elevate through the molten glass, reach the surface ofthe molten glass, and disappear. As a result, a gas component at thesurface of the molten glass is entrained, to cause countless entrainedbubbles on the surface of the molten glass. Thus, fine bubble defectsare generated on the melt surface to waste a fining effect foreliminating fine bubbles of helium or neon to provide homogeneous glass.An average diameter of bubbles containing helium and/or neon ispreferably 150 mm or less, more preferably 120 mm or less, still morepreferably 100 mm or less, yet more preferably 80 mm or less.

The type of refractory material to be used for the glass melting furnaceof the present invention is not particularly limited as long as theglass melting furnace of the present invention has required heatresistance and the refractory material is capable of maintainingstructural strength at high temperatures with time. The refractorymaterial often employs ceramics or a heat resistant metal. However,because there are many porous refractory materials, attention must bepaid such that materials that carelessly dissipate helium or neon out ofthe glass melting furnace are not used in positions where helium or neonis to be retained.

The method, means, or device for heating is not particularly limited forthe heating means that can be employed in the glass melting furnace ofthe present invention. The heating means may employ indirect heating ordirect heating. The heating means may employ a method of heating byelectricity, burning of various fuels, or electromagnetic wave. Onemethod may be used, or a plurality thereof may be used in combination.The heating device needs to have no reactivity inhibiting avitrification reaction, cause no problems in structural strength at hightemperatures, have a size allowing heating of glass raw materials atonce in a volume in accordance the purpose, and be constructed withconstruction materials in accordance with the purpose of melting a glassmaterial.

The glass material that can be melted in the glass melting furnace ofthe present invention generally contains multicomponent oxides ofinorganic elements as main components. Here, the glass materialcontaining multicomponent oxides of inorganic elements as maincomponents indicates that the glass material contains two or more typesof oxides and intentionally contains a total amount of the two or moretypes of oxides of 50% or more in mass %. A glass composition containinga single component and a plurality of components mixed as impuritiesdoes not correspond to the multicomponent oxides of the presentinvention. For example, a glass composition containing a singlecomponent in a content of about 99% in mass % and a plurality ofcomponents in a content in hundredths, that is, a content of 0.09 mass %or less does not correspond to the glass material containingmulticomponent oxides. Thus, the present invention is not applied toquartz glass for optical fiber or high purity quartz glass similarthereto. The present invention is not applied to non oxide glass such asfluoride glass or fluoride phosphate glass containing a large amount offluorine as anions, chalcogenide glass, chalcohalide glass, oroxynitride glass.

The uses for the glass manufactured through the present invention arenot particularly limited. That is, the glass of the present invention issuitable for manufacture of glass products requiring high technologysuch as: sheet glass for a substrate of a liquid crystal displayelement; sheet glass used for a plasma display; cover glass forpackaging a solid image sensor; tube glass for backlight installed in aliquid crystal display; high strength crystallized glass; various lenscomponents used for optical components; and low melting point powderglass.

A glass composition to be manufactured by using the glass manufacturingapparatus of the present invention, that is, a glass product containingmulticomponent oxides manufactured by melting glass raw materials hassuch a feature that a helium and/or neon content is 0.0001 to 2 μl/g (0°C., 1 atm). Helium and/or neon present in the glass product is in astate of being trapped in interstices of a glass network structureconstructed by other glass components. The present invention refers tosuch a state as a state of being dissolved in glass.

Bubble diameters are measured by: photographing bubbles through aneoceram window, which is transparent crystallized glass for observinginside of a furnace, by using a photographic device for photographing athigh temperatures; and subjecting image data to image analysis forcalculation. A helium and/or neon content in the glass can be measuredwith a quadrupole mass spectrometer. Gas analysis with the quadrupolemass spectrometer involves: placing a glass sample for measurement intoa platinum plate; retaining the platinum dish in a sample chamber undervacuum of 10⁻⁵ Pa (that is, 10⁻⁸ Torr); heating the platinum dish; anddirecting a gas discharged after the heating to the quadrupole massspectrometer having a measurement sensitivity of 0.0001 μL/g foranalysis.

The present invention provides the following effects.

(1) The glass melting furnace of the present invention allows rapid andefficient diffusion and mixing, and dissolution of helium and/or neoninto the molten glass, and thus provides a fining effect on bubbles ofvery small diameters of 0.1 mm or less in the molten glass, which arehardly fined.

(2) The glass melting furnace of the present invention has aconcentration of helium and/or neon to be dissolved of 0.0001 μl/g (0°C., 1 atm) or more, and thus is capable of effectively advancing finingof glass and reducing a time period required for forming a homogeneousglass state.

(3) The glass melting furnace of the present invention has the noble gasdissolving means at least partially immersed in the molten glass, andthus is capable of bringing helium and/or neon into contact with themolten glass in a state of being most easily diffused and mixed, andrealizing an optimal fining effect.

(4) The glass melting furnace of the present invention has the noble gasdissolving means provided in at least one position selected from theinside, upper side, lower side, and side of the molten glass, and thuscan be applied to manufacturing processes corresponding to variousmelting or forming systems. The glass melting furnace employing amelting system in accordance with market demands and productspecifications allows abundant supply of a glass product havingsufficient properties.

(5) The glass melting furnace of the present invention has the noble gasdissolving means including at least one device selected from the groupconsisting of a heating device, a pressure reducing device, and acentrifugal force generating device, and thus is capable of employingthe best method in accordance with the properties of the molten glassproduct as required. The glass melting furnace allows manufacture of ahigh quality glass product at low manufacturing cost by realizing themaximum fining effect with small energy.

(6) The glass melting furnace of the present invention has the heatingmeans including at least one tank constituted by a heat resistantvessel, and thus is capable of attaining finally stabilized fining by:retaining and heating the molten glass; assuredly directing a dissolvedgas out of a molten glass system for a glass product having anycomposition; and continuing degassing as long as the molten glass ispresent in the vessel.

(7) The glass melting furnace of the present invention has the noble gasdissolving means generating a flow of a helium and/or neon gas in adirection at a vector angle of 0° to 80°, 50° to 130°, or 100° to 180°with respect to a flow direction of the molten glass, and thus iscapable of performing fining of various glass materials at a high levelby optimally setting a flow direction based on whether the glassmaterial allows easy diffusion and mixing of helium and/or neon or not.

(8) The glass melting furnace of the present invention has the noble gasdissolving means formed of a heat resistant metal and/or ceramics, andthus is capable of realizing stable manufacture of glass over a longperiod of time.

(9) The glass melting furnace of the present invention further includesthe noble gas degassing means provided in at least one position selectedfrom the inside, upper side, lower side, and side of the molten glass,and thus is capable of assuredly removing bubbles remained in the moltenglass by rapidly degassing helium and/or neon diffused and mixed in themolten glass. The glass melting furnace allows efficient manufacture ofa high quality glass product having a high viscosity, which is hardlyformed into homogenous glass through a conventional fining method.

(10) The glass melting furnace of the present invention has the noblegas degassing means including at least one device selected from thegroup consisting of a heating device, a pressure reducing device, and acentrifugal force generating device, and thus is capable of assuredlyperforming a degassing operation from the molten glass allowing forselection of the device in accordance with not only the type of glassbut also the use or required production of the glass.

(11) The glass melting furnace of the present invention allows efficientrecycling of helium or neon generated through fining of the moltenglass, and efficient use of an expensive helium or neon gas.

(12) The glass melting furnace of the present invention has the noblegas dissolving means provided with a plurality of noble gas inlets, andthus is capable of easily adjusting an introducing volume of helium orneon into the molten glass. The glass melting furnace allows massproduction of a glass product having stable quality through preciseadjustment under various furnace operation conditions of the glassmelting furnace.

(13) The glass melting furnace of the present invention has theplurality of noble gas inlets provided on a hearth and/or on a furnacewall, and thus is capable of easily introducing helium or neon into thefurnace without disordering a flow state of the molten glass in thefurnace or greatly affecting the furnace temperature conditions, and ofpreventing reduction in life of manufacturing apparatus or peripheraldevices due to introduction of helium or neon.

(14) The glass melting furnace of the present invention has theplurality of noble gas inlets each formed of a metal having a meltingpoint of 1,000° C. or higher, and thus inhibits deformation ordeterioration of the noble gas inlets in use over a long period of time,allows a steady volume of the noble gas to be introduced into thefurnace or stable flow of the noble gas introduced, and allowssufficient intervals between periodic maintenance of the noble gasinlets.

(15) The glass melting furnace of the present invention has the noblegas dissolving means provided in a noble gas dissolving tank connecteddownstream of the melting tank, and thus is capable of assuredly andeffectively performing fining by introduction of helium or neon. Theglass melting furnace has the noble gas dissolving tank having an innerwall surface formed of a refractory brick having a refractorytemperature of 1,200° C. or higher, or a heat resistant metal having amelting point of 1,200° C. or higher, and thus is capable of maintaininga state realizing homogeneous glass through fining by introduction ofhelium or neon for a sufficiently long period of time.

(16) The glass melting furnace of the present invention has therefractory brick containing at least one selected from the groupconsisting of SiO₂, ZrO₂, Al₂O₃, MgO, Cr₂O₃, C, and WO₃, or the heatresistant metal containing at least one metal selected from the groupconsisting of Pt, Ir, Os, Re, W, Ta, Rh, Hf, Ru, Tc, Pd, Mo, Ti, Zr, andNb, and thus is capable of preventing melting of refractory brick orheat resistant metal into the glass or outflow of foreign substances asa glass defect by arbitrarily selecting an optimal material inconsideration of various components in the glass, melting temperature,required high temperature strength with time, and the like.

(17) The method of manufacturing glass of the present invention allowsrapid and efficient diffusion and mixing, and dissolution of heliumand/or neon into the molten glass.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a glass melting furnace according to anembodiment of the present invention. FIG. 1 (X1) is a sectional view(taken along the line X1-X1 of FIG. 1(Y)) of the glass melting furnaceseen from a side. FIG. 1 (X2) is a partially sectional view (taken alongthe line X2-X2 of FIG. 1(Y)) of a peripheral part of a noble gasdissolving device. FIG. 1(Y) is a sectional view of the glass meltingfurnace seen from an upper side.

FIG. 2 is a partially sectional view of a noble gas dissolving deviceaccording to another embodiment of the present invention.

FIG. 3 is a partially sectional view of a noble gas dissolving deviceaccording to still another embodiment of the present invention.

FIG. 4 is a sectional view taken along the line E-E of FIG. 3.

FIG. 5 is a partially sectional view of a noble gas dissolving deviceaccording to yet another embodiment of the present invention.

FIG. 6 is a partially sectional view of a noble gas dissolving deviceaccording to still yet another embodiment of the present invention.

FIG. 7 is an explanatory drawing regarding a test of the presentinvention performed in a laboratory.

FIG. 8 is an explanatory drawing regarding another test of the presentinvention performed in a laboratory.

FIG. 9 is a partially sectional view of a noble gas dissolving deviceaccording to an embodiment of the present invention.

FIG. 10 is a sectional view of a glass melting furnace according toanother embodiment of the present invention seen from a side.

FIG. 11 is a sectional side view of a conventional continuous meltingfurnace.

FIG. 12 is a sectional side view of a conventional batch furnace.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, a glass melting furnace and method of manufacturing glassaccording to the present invention will be described in detail based onexamples.

EMBODIMENT 1

The inventors of the present invention have attempted to improve productyield than before by: applying the glass melting furnace of the presentinvention as a melting device for a glass product, which is silicateglass of a composition having an alkali content of 10 mass % or less andused as sheet glass for electronic components; and assuredly performingfining of the glass. The glass melting furnace of the present inventionwas realized by providing a noble gas dissolving device as noble gasdissolving means for diffusing and mixing, and dissolving helium and/orneon into molten glass, between a melting tank and fining chamber of asmall continuous melting furnace conventionally used. FIG. 1 shows aconstitution of a glass melting furnace 1. A refractory wall is providedbetween a melting tank 10 and a fining chamber 30. Molten glass G in themelting tank 10 flows into the fining chamber 30 through two noble gasdissolving devices 5 {see FIG. 1(Y)} respectively connected to both sidewalls of the melting tank 10.

A glass manufacturing process in the glass melting tank 1 is asdescribed below. First, a glass raw material B for glass melting isprepared by weighing a plurality of raw materials satisfying desiredspecifications such as grain size, impurities, and water content, andmixing the plurality of raw materials homogeneously. At this time, abroken glass cullet is prepared in advance as a mixed batch as required.The glass raw material B is charged into the melting tank 10 with a rawmaterial charging machine provided at a raw material inlet 11. Theintroduced glass raw material B is melted by heating with a sheet-likeelectrode 12 and a burner 31 in the melting tank 10. Molten glass G inliquid form through melting elevates in the tank through a throat part40, then flows into the noble gas dissolving devices 5 respectivelyconnected to both sides of the melting tank 10.

To exits of the molten glass G of the noble gas dissolving devices 5, ahelium gas A is introduced through platinum/rhodium noble gas inlets 22by directing heat resistant gas introduction tubes 21 from the outsideof the furnace. The introduced helium gas A moves in the noble gasdissolving devices 5 while maintaining a flow direction at a vectorangle of 180° with respect to a flow direction of the molten glass G.The helium gas A has gas ascending force in addition to diffusion forceof the helium gas A itself, and moves while generating turbulence in thevicinity thereof with elevation of helium bubbles. The helium gas A isbrought into a state of being easily dissolved in the molten glass G intilted tubular paths inside the noble gas dissolving devices 5,partially diffused into the molten glass G, mixed by the turbulence, anddissolved in an atomic state. The helium gas A that remains undissolvedis deaerated, degassed, and collected through a gas discharge tube 13for collecting the helium gas provided at a ceiling of the melting tank10 as a part of noble gas degassing means. The gas discharge tube 13 isconnected to a device (omitted in the figure) having a heat resistantpumping function capable of adjusting a gas volume to be collected. Agas from expanded bubbles can be collected by sucking a helium gasdissolved in the molten gas G while an excess gas is collected. The gasdischarge tube 13 also has a function of so-called a degassing device15. The glass melting furnace employs a structure provided with twonoble gas dissolving devices 5, and the two noble gas dissolving devicesmay be operated or one may be operated in accordance with a production.

The molten glass Gin the melting tank 10 contains fine bubbles,supersaturated reaction gas components, and the like, and the helium gasacts on the fine bubbles to expand the bubbles by being diffused andmixed, and dissolved in the molten glass G. Helium atoms are diffusedand mixed into the molten glass G to form bubbles of the supersaturatedreaction gas components of the glass raw materials, which are expandedand deaerated. A part of the undeaerated helium atoms remains trapped ina network constructed by glass components.

The sufficiently fined molten glass G flows into a feeder 50 from thefining chamber 30, and is homogeneously mixed with two stirrers 51provided in the feeder 50. Then, the molten glass G is formed into thinsheets with rolls (omitted in the figure) in a downstream formingregion. The thus-manufactured sheet glass for electronic componentsconventionally had a rate of bubble defects of 7%. The thus-manufacturedsheet glass for electronic components had a rate reduced to 0.2% withthe glass melting furnace 1 of the present invention, to allowmanufacture of sheet glass for electronic components having highquality. A helium content in the glass was 0.055 μl/g (0° C., 1 atm),which was a content within a predetermined range of 0.01 to 2 μl/g (0°C., atm).

EMBODIMENT 2

Next, an embodiment employing a constitution suitable for melting aglass material having easier properties of diffusion and mixing, anddissolution of helium and/or neon into the molten glass compared withEmbodiment 1 as a glass melting furnace for tubular glass used forelectronic components is described.

The melting furnace is very small as a continuous melting furnace, andhas a disadvantage that unreacted raw material components are apt toflow out to the fining chamber because of a small volume of the meltingtank. In order to overcome the disadvantage, the melting furnace employsa structure having a noble gas dissolving device connected downstream ofthe melting tank. FIG. 2 shows a partially sectional view of a noble gasdissolving device 6 employed in the glass melting furnace.

The molten glass G melted in the melting tank flows into the noble gasdissolving device 6 from the left side of FIG. 2. Meanwhile, the heliumgas A is introduced in an opposite direction at a vector angle of 180°with respect to the flow direction of the molten glass G. The heatresistant gas introduction tube 21 employs a platinum/rhodium alloy, andbubbles are controlled to have an average diameter of 60 mm or less bynarrowing a tip part and arbitrarily adjusting a flow rate. The heliumgas A is introduced from a direction opposite to the flow of the moltenglass G, to thereby allow rapid progress of mixing and dissolution ofhelium atoms into the molten glass G. The diameters of the bubbles ofthe gas derived from the remaining glass supersaturated through thereaction of glass raw materials expand through diffusion of the heliumgas A, to thereby accelerate deaeration of bubbles from the molten glassG.

The remaining helium gas A is accumulated in a gas accumulation chamber80 in an upper part of the noble gas dissolving device 6 as a part ofthe noble gas degassing means, and is collected through the gasdischarge tube 13 provided here. The collected gas has hightemperatures, and preheating of the helium gas A to be introduced isperformed by utilizing the heat. That is, a double tube structureallowing a flow of a waste gas outside of the heat resistant gasintroduction tube 21 is employed, to thereby allow efficient operation.

Finally, the molten glass G is homogeneously mixed with a stirrer 51,which is a stirring device provided downstream of the noble gasdissolving device 6, into a state of having no insufficiently mixedparts. The molten glass G flows out of the noble gas dissolving device6, flows into the fining chamber, flows through the fining chamber, andreaches the forming region, to thereby allow forming of the tubularglass.

The conventional manufactured tubular glass for electronic componentshad about 10 bubbles of very small diameters of about 0.2 mm per 100 gof glass. The thus-manufactured tubular glass for electronic componentshad an improved rate of bubble defects of about 0.1 bubble per 100 gglass, and profitable products were able to be supplied in accordancewith market demands because of reduced rate of bubble defects. A heliumcontent in the glass was 0.046 μl/g (0° C., 1 atm), which was a contentwithin a predetermined range of 0.001 to 2 μl/g (0° C., atm).

EMBODIMENT 3

Next, an embodiment employing a glass melting furnace of the presentinvention as an apparatus for manufacturing display glass is described.Because bubbles in an image display part are highly visible, glassproducts used for such an application require stricter management ofbubble quality than that of glass products used for other applications,and bubbles are perceived as critical defects. FIG. 3 shows alongitudinal sectional view of a noble gas dissolving device 7 providedin the glass melting furnace of the present invention, and FIG. 4 showsa transverse sectional view of the E part of FIG. 3. The raw materialscharged into the melting tank are melted by heating with a burner and bydirect heating with a platinum electrode, and the molten glass G flowsinto the noble gas dissolving device 7 from the left side of FIG. 3. Asshown in FIGS. 3 and 4, heat resistant tubs 23 are provided inside thenoble gas dissolving device 7. While the molten glass G flows along theheat resistant tubs 23, the helium gas A is introduced in a flowdirection at a vector angle of 180° from the heat resistant gasintroduction tube 21 provided in an upper side of the molten glass G.The helium gas A is diffused and mixed into the molten glass G in theheat resistant tubs 23, and dissolved as helium in an atomic state.

An upper part of the molten glass G in the noble gas dissolving device 7is filled with the introduced helium gas A, to thereby realize anenvironment facilitating diffusion and mixing, and dissolution of thehelium gas A into the molten glass G while the molten glass G falls fromthe heat resistant tubs 23. In this way, helium atoms are dissolved inthe molten glass G, and act on bubbles of very small diameters remainedin the molten glass G to expand. Then, the molten glass G flows out tothe fining chamber provided on the right side of FIG. 3, to therebyaccelerate fining of the molten glass.

The glass melting furnace of the present invention as shown in FIGS. 3and 4 is used, to thereby reduce a rate of fine bubble defects, whichcauses problems in the image display part, by 9% compared with that ofthe conventional melting furnace and allow supply of glass products fordisplay devices and having high quality.

EMBODIMENT 4

If powder glass used for displays or the like has fine bubbles in theglass, the powder glass may foam when a glass member for display or thelike is sealed with the powder glass and may cause problems of affectingvarious properties such as strength and brightness of the display. Thus,the inventors of the present invention have conducted studies on whetherthe glass melting furnace of the present invention can be applied tomelting of such powder glass.

Two embodiments which attempt to provide the noble gas dissolving devicein the glass melting furnace are described. FIG. 5 shows a partiallysectional view of the fining chamber 30 of the glass melting furnaceprovided with a noble gas dissolving device 8, and FIG. 6 shows apartially sectional view of a noble gas dissolving device 9. The noblegas dissolving device 8 of FIG. 5 was initially used. In this case,after the raw materials are melted in the melting tank, the molten glassG flows into the fining chamber 30 from the left side of FIG. 5. Thenoble gas dissolving device 8 is provided to be immersed in the moltenglass G in the fining chamber 30. A gas containing 5% neon and 95%helium in volume ratio is introduced from an upper part of the finingchamber 30 through the platinum/rhodium gas introduction tube 21. Thegas is blown out from the platinum/rhodium noble gas inlet 22,accumulated in the tank, and heated by the molten glass G in thevicinity thereof. The gas converts into helium/neon mixed gas bubbles byascending force from the vicinity of the noble gas dissolving device 8,and elevates in a direction at a vector angle of 90° with respect to aflow direction of the melting glass G.

A fining effect in the noble gas dissolving device 8 was significantlyimproved compared with that of the melting furnace employing no noblegas dissolving device 8 with a bubble generation rate reduced by 12%during a final sealing test. However, substantial modifications weremade to provide a structure as shown in FIG. 6, for attaining a finingeffect at a higher level. FIG. 5 employs a structure provided with thenoble gas dissolving device 8 in the fining chamber 30. FIG. 6 employs astructure provided with a noble gas dissolving device 9 between themelting tank 10 and the fining chamber 30 by changing a structureallowing introduction of the helium gas A in the fining chamber 30 ofFIG. 5 to a structure allowing introduction of the helium gas A into themolten glass G at a position further upstream. The molten glass Gsubjected to primary glass melting reaction in the melting tank 10 flowsinto the noble gas dissolving device 9 from the left side of FIG. 6, andis provided with rotational motion with a platinum/rhodium stirrer 51driven by an upper part of the noble gas dissolving device 9. Meanwhile,the helium gas A is preheated and introduced into the noble gasdissolving device 9 from a lower part of the stirrer 51. The helium gasA elevates in a direction at a vector angle of 90° with respect to aflow direction of the molten glass G generated by the stirrer 51. Thehelium gas A is diffused and mixed, and dissolved in an atomic statewhile passing and elevating through the stirrer 51. The excess heliumgas A is collected through the gas discharge tube 13, which is a part ofthe degassing device, and is recycled.

The molten glass G passes through a throat-like structure in the noblegas dissolving device 9, is mixed into a homogeneous state with thestirrer 51, and then flows into the fining chamber 30.

The glass melting furnace of the present invention provided withimprovements as shown in FIG. 6 is employed, to thereby provide anadditional reducing effect on a bubble generation rate and allowmanufacture of a homogenous and sufficiently fined glass product.

EMBODIMENT 5

Final improvements on mode of FIG. 6 were made by conducting apreliminary test in a laboratory for providing improvements as shown inFIG. 6. FIG. 7 shows an explanatory drawing regarding equipment used forthe preliminary test.

The same powder glass for display or the like as that melted in theglass melting furnace of FIG. 5 was used in the test. The gas is bubbledin the molten glass G for the purpose of diffusing the helium gas A intothe molten glass G. In the test, the helium gas A is introduced bybubbling the gas into the molten glass G from the platinum/iridium noblegas inlet 22 provided at the tip of the heat resistant bubbling tube(that is, the gas introduction tube 21) provided in the vicinity of abottom of a platinum crucible 70. A flow of the molten glass G at avector angle of 90° with respect to bubbles of the helium gas Aelevating through the molten glass G is formed, and the bubblesthemselves are broken into bubbles having reduced diameters in themolten glass G with spinning blades of the stirrer 51, to thereby obtainbubbles having a sphere equivalent average diameter of 40 mm or less.Thus, an elevating of bubbles is reduced in the molten glass G, tofacilitate contact between the helium gas A and the molten glass G overa long period of time.

As a result, a helium content in the glass after the test was increasedby 20% compared with that in the glass obtained by simply bubbling thehelium gas A from the bottom of the crucible 70 regardless of the samehelium flow rate. Further, the final bubble content in the glass wasimproved compared with that in the glass obtained by introducing thehelium gas A through simply bubbling. A heat reboiling test of theobtained glass confirmed no concern of reboiling, and the glass hadexcellent quality.

EMBODIMENT 6

Next, based on the results of FIG. 5, the following tests were conductedfor realizing effective bubbling of bubbles having even smallerdiameters. The test was conducted for a composition of capillary glassused for lamps. FIG. 8 shows an explanatory drawing regarding testequipment.

Based on the results of Embodiments 4 and 5, a bubble diameter wasfurther reduced to a sphere equivalent average diameter of 30 mm orless, and the stirrer 51 having both functions of the heat resistant gasintroduction tube 21 and a stirrer was designed. Studies were conductedon whether efficient manufacture is possible by using the stirrer. Thestirrer 51 having a rotational axis of a tubular shape was employed,which allows introduction of the helium gas A into the molten glass Gfrom the platinum noble gas inlet 22 provided at the tip of the stirrer51.

It was confirmed that the bubble diameter of the helium gas A can bereduced by: bubbling helium into the molten glass G maintained at 1,400°C. from the stirrer 51 provided as shown in FIG. 8; and rotating thestirrer 51.

The molten glass G melted in advance at 1,400° C. or 1,350° C. for 2hours was poured into the platinum/rhodium crucible 70 while the glasshad a high temperature, and helium was bubbled from the noble gas inlet22 provided at the tip of a stirrer-type helium introduction tube 51(21) at 1,400° C. for 2 hours. The number of bubbles were measured,resulting in 10 to 50 bubbles/kg for the molten glass heated to 1,400°C. to 1,400° C., and 0 to 10 bubbles/kg for the molten glass heated to1,350° C. to 1,400. As a result, findings providing effectivemanufacture conditions were able to be obtained by using the stirrer 51and employing helium bubbling.

EMBODIMENT 7

Next, an embodiment employing the glass melting furnace of the presentinvention as a glass melting furnace for manufacture of glass productsused for optical components is described. Because the glass ismanufactured through a batch process using a platinum pot 70, has a highrate of bubble defects of about 16%, and has a low product yield, theinventors of the present invention have attempted to apply the presentinvention as a countermeasure. As shown in FIG. 9, a noble gasdissolving device 52 is immersed in the molten glass G, and the heliumgas A is blown out from the noble gas inlet 22 to introduce the heliumgas A into the noble gas dissolving device 52 in the molten glass G. Theintroduced helium gas A is stirred with blades inside the noble gasdissolving device 52 to provide bubbles having an average diameter of 50mm or less. A flow of the helium gas A is generated in a direction at avector angle of 90° with respect to the flow of glass in an upwarddirection generated by convention. The helium gas A is diffused andmixed into the molten glass G, and thus is dissolved into the moltenglass G in an atomic state.

The present invention was applied, to thereby reduce a rate of bubbledefects to about 8%, which was conventionally about 16%, improve productyield, and reduce product cost. A measured helium content in the glasswas 0.033 μl/g (0° C., 1 atm), which was a content within apredetermined range of 0.001 to 2 μl/g (0C, atm). The present inventionwas applied to facilitate fining of the glass, which conventionally haddifficulties in fining, and allow supply of homogenous glass inaccordance with market demands.

EMBODIMENT 8

Finally, an embodiment employing the melting furnace and method ofmanufacturing glass of the present invention for manufacture of thinsheet glass installed in an image display part of a liquid crystaldisplay device is described.

Non-alkali glass has been manufactured by using a relatively large glassmelting furnace, but improvements for redesigning a melting device intoa high capacity melting device have been required with recent technicalinnovation and market expansion. The inventors of the present inventionhave attempted to improve the glass melting furnace into the glassmelting furnace of the present invention providing good results invarious tests, in addition to a series of improvements on such a device.

FIG. 10 shows a sectional view of the glass melting furnace after theimprovement. The glass raw material B is mixed with a large raw materialmixer, supplied to a screw charging machine provided at the raw materialinlet 11 by a belt conveyor, and charged into the melting tank 10 of theglass melting furnace at a predetermined rate. In the melting tank 10,the charged glass raw material B is melted by heating with the burner 31and by heating with the electrode 12, to form the molten glass G. Then,the molten glass G flows into a tank additionally provided as a noblegas dissolving tank 20 through a throat 40. The noble gas dissolvingtank 20 is provided with a noble gas dissolving device 53 (referred toas a bubbler module 53). The bubbler module 53 is provided with aplurality of, for example, sixteen noble gas inlets 22 for introducing ahelium gas or neon gas supplied to a hearth by the heat resistant gasintroduction tubes 21 into the noble gas dissolving tank 20 (FIG. 10shows four noble gas inlets 22 aligned in a flow direction of the moltenglass, but the noble gas inlets 22 are arranged in four rows in adirection perpendicular to the flow direction of the molten glass. Atotal of sixteen inlets are provided.). Each of the noble gas inlets 22on the hearth of the bubbler module 53 is coated with a 15% platinum(Pt)/rhodium (Rh) alloy. A density of the noble gas inlets 22 providedin the bubbler module 53 is set to 10,000 inlets/m² or less.

From the bubbler module 53 having sixteen noble gas inlets 22, bubblesof the helium gas A having a purity of 99% are blown into the moltenglass G at a supply volume providing an average bubble diameter of 80 mmor less, to thereby cause diffusion of helium atoms from the heliumbubbles into the molten glass G. The noble gas dissolving tank 20 isprovided with an electrode (omitted in the figure) or the gas dischargetube 13 in addition to the bubbler module 53, and the helium gasaccumulated above the molten glass G may be collected after the heliumgas is blown out from the bubbler module 53 and elevates through themolten glass G. The noble gas melting tank 20 employs electrocastrefractory bricks containing 80 mass % or more zirconia as refractorymaterials for the inner wall and hearth of the tank such that the noblegas melting tank 20 can be heated to high temperatures of 1,500° C. orhigher. A high temperature part of a metal line (line representing aninterface between molten glass and melting atmosphere on a furnace wall)employs a refractory material coated with platinum. This coating is forpreventing fluctuation of the metal line by the helium gas or neon gasblown out from the bubbler module to cause significant progress incorrosion of the refractory material in the metal line part.

Even in the noble gas dissolving tank 20, a part of a fining reactionfor releasing fine reaction bubbles in the molten glass G starts. Actualfining is performed by heating the molten glass G in the fining chamber30 after the molten glass flows out of the noble gas dissolving tank 20,to thereby form homogenous molten glass. The molten glass G flows into afeeder 50, and is subjected to final homogenization operation with astirrer 51. The molten glass G flows into a forming region, to be formedinto thin sheet glass.

Such a glass melting furnace is used to allow reduction of bubbles eachhaving a fine size causing problems in forming of thin sheet glass witha large area and improvement in efficiency percentage. Such a glassmelting furnace provides glass having a helium content falling within apredetermined range of 0.0001 to 2 μl/g (0° C., atm).

1. A glass melting furnace for melting glass raw materials by heating toform molten glass, characterized by comprising: an inlet for chargingglass raw materials; an outlet for taking out molten glass; a meltingtank for retaining the glass raw materials and the molten glass for apredetermined period of time; heating means for heating the glass rawmaterials and molten glass charged into the melting tank; and noble gasdissolving means for supplying helium and/or neon from a noble gasinlet, and diffusing and mixing helium and/or neon into the molten glassto dissolve a predetermined concentration or more of helium and/or neonin the molten glass.
 2. A glass melting furnace according to claim 1,characterized in that a concentration of helium and/or neon to bedissolved is 0.0001 μl/g (0° C., 1 atm) or more.
 3. A glass meltingfurnace according to claim 1, characterized in that the noble gasdissolving means is at least partially immersed in the molten glass. 4.A glass melting furnace according to claim 1, characterized in that thenoble gas dissolving means is provided in at least one position selectedfrom an inside, upper side, lower side, and side of the molten glass. 5.A glass melting furnace according to claim 1, characterized in that thenoble gas dissolving means contains at least one device selected fromthe group consisting of a heating device, a pressure reducing device,and a centrifugal force generating device.
 6. A glass melting furnaceaccording to claim 5, characterized in that the heating device comprisesat least one tank constituted by a heat resistant vessel.
 7. A glassmelting furnace according to claim 1, characterized in that the noblegas dissolving means generates a flow of a helium and/or neon gas in adirection at a vector angle of 0° to 80°, 50° to 130°, or 100° to 180°with respect to a flow direction of the molten glass.
 8. A glass meltingfurnace according to claim 1, characterized in that the noble gasdissolving means is formed of a heat resistant metal and/or ceramics. 9.A glass melting furnace according to claim 1, characterized by furthercomprising noble gas degassing means for degassing a gas containinghelium and/or neon from the molten glass after helium and/or neon isdiffused and mixed into the molten glass, which is provided in at leastone position selected from the inside, upper side, lower side, and sideof the molten glass.
 10. A glass melting furnace according to claim 9,characterized in that the noble gas degassing means comprises at leastone device selected from the group consisting of a heating device, apressure reducing device, and a centrifugal force generating device. 11.A glass melting furnace according to claim 10, characterized in that thenoble gas degassing means includes a noble gas collection chamberprovided on the upper side the molten glass.
 12. A glass melting furnaceaccording to claim 1, characterized in that the noble gas dissolvingmeans is provided with a plurality of noble gas inlets.
 13. A glassmelting furnace according to claim 11, characterized in that theplurality of noble gas inlets are provided on a hearth and/or on afurnace wall.
 14. A glass melting furnace according to claim 13,characterized in that the plurality of noble gas inlets are each formedof a metal having a melting point of 1,000° C. or higher.
 15. A glassmelting furnace according to claim 1, characterized in that the noblegas dissolving means is provided in a noble gas dissolving tankconnected downstream of the melting tank.
 16. A glass melting furnaceaccording to claim 15, characterized in that a fining chamber isconnected downstream of the noble gas dissolving tank.
 17. A glassmelting furnace according to claim 15, characterized in that the noblegas dissolving tank has an inner wall surface formed of refractorybricks having a refractory temperature of 1,200° C. or higher, or a heatresistant metal having a melting point of 1,200° C. or higher.
 18. Aglass melting furnace according to claim 17, characterized in that therefractory brick contains at least one selected from the groupconsisting of SiO₂, ZrO₂, Al₂O₃, MgO, Cr₂O₃, C, and WO₃.
 19. A glassmelting furnace according to claim 17, characterized in that the heatresistant metal contains at least one selected from the group consistingof Pt, Ir, Os, Re, W, Ta, Rh, Hf, Ru, Tc, Pd, Mo, Ti, Zr, and Nb.
 20. Amethod of manufacturing glass for melting glass raw materials by heatingto form molten glass, characterized by comprising: introducing bubblescontaining helium and/or neon and having an average diameter of 150 mmor less into molten glass; and diffusing and mixing helium and/or neoninto the molten glass to incorporate a predetermined volume of heliumand/or neon in the molten glass.